1. Field of the Invention
The present invention concerns an apparatus for perforating corrugated tubing. More particularly, the present invention concerns the perforating dual wall corrugated tubing.
2. Prior Art
Machines for perforating tubing are known. U.S. Pat. No. 3,824,886 issued Jul. 23, 1974 to Hegler, teaches an apparatus for cutting apertures in corrugated tubing by rotating the cutter circumferentially around the tubing. The cutter is disposed within a ridge on a wheel, which is driven by a transmission. The wheel and cutter cooperate with a roller to rotate about the tubing. The cutter travels in an epitrochoidal path around the outer surface of the tubing, causing a perforation where the cutter strikes the tubing. Hegler achieves perforations perpendicular to the axis of the tubing by this method.
While offering a relatively simple design to achieve its ends, Hegler is necessarily limited to perforating corrugated tubing at relatively low speeds due to the necessity of the wheel and cutter traveling the entire length of the corrugation. Increasing the traveling speed of the wheel beyond modest levels would result in miscuts in the tubing, such as cuts in the side walls of the corrugation instead of the valley thereof. Further, excessive wheel speed would cause the wheel to jump past corrugations, thus missing areas of the tubing and leaving these areas unperforated. Hegler does not address the issue of perforating dual wall piping.
U.S. Pat. No. 4,180,357 issued Dec. 25, 1979 to Lupke et alia teaches an apparatus for perforating tubing. Lupke et alia teaches a machine having a plurality of lead screws for driving the tubing along an axial path, the lead screws meshingly engaging with the corrugations of the tubing. Each lead screw is mounted on an axis of rotation parallel to the axial path of the tubing. Mounted upon each lead screw is a cutter, flanked on each side by a raised rib. The cutter is in a plane substantially at a right angle to the axial path and the cutter intermittently intersects the tubing. Lupke achieves rotation of the lead screws by a system of gear wheels coordinated such that pairs of lead screws cut the tubing simultaneously. Lupke can achieve a maximum horizontal tubing speed of 20 feet per minute while cutting. At speeds greater than 20 feet per minute, the apparatus of Lupke experiences difficulty in realigning the cutter and properly perforating the tubing.
U.S. Pat. No. 4,218,164 issued Aug. 19, 1980 to Lupke et alia teaches an improvement upon the previous Lupke apparatus of the '357 patent. The plurality of lead screw members have a helically raised rib member mounted centrally thereon, the helical rib replacing the raised straight ribs of the previous apparatus. The cutter is disposed at the end of the helical rib. The helical rib tends to facilitate entry of the cutter into the valley of the corrugation. The rib extends around only a portion of the circumference of the shaft, thus continuing the teaching of intermittent intersection by the cutter as taught in the previous Lupke patent. This apparatus achieves a horizontal tubing speed of approximately 40 to 50 feet per minute. At speeds in excess of 50 feet per minute, the apparatus tends to climb the side walls of the corrugation and perforate either those walls or the crown of the corrugation.
The devices of the Lupke et alia patents overcome the limitation of rotating the entire cutter wheel around the tubing as taught by Hegler. In the first Lupke patent, the plurality of raised ribs essentially slowed the horizontal movement of the tubing long enough to effect the perforation. The apparatus of the second Lupke patent substituted the helical rib for the plurality of straight ribs. This alleviated the need to slow or stop the horizontal travel of the tubing along the axial path to effect the perforation, and works relatively well at lower speeds, i.e. speeds less than 50 feet per minute.
However, both Lupke apparatuses encounter serious problems when greater speeds are attempted. When operated at speeds in excess of 50 feet per minute, the cutter of the first Lupke apparatus is not able to spring back to its original start position for the next intermittent engagement of the tubing. Thus, the cutter is not able to perforate the valley of the corrugation, but rather cuts into the side wall, miscutting the tubing. Similar problems occur with the second Lupke apparatus.
Additionally, problems are encountered with the feed worms of Lupke. At high speeds, the vertical sides of the feed worms are unable to maintain their helical course in the corrugation. Thus, the worms tend to climb the side walls of the corrugations, crushing the crown of the tubing and skipping parts of the corrugation. These problems are amplified by attempts to cut non-flexible tubing, such as dual wall tubing.
Different problems are encountered when tubing is a dual wall construction. Dual wall tubing has corrugation on the outer surface thereof, while having a smooth, substantially hard inner cylindrical surface. Such tubing, having significantly greater rigidity, is more difficult to perforate.
Dual wall tubing, like other corrugated tubing, is often perforated immediately after being produced by an extrusion machine. The tubing comes at a non-constant rate due to the production process. This presents a potentially serious problems, since reductions or increases in tubing production will affect the tubing perforation. In flexible corrugated tubing, this problem is addressed by increasing or decreasing the cutting of the perforator by a potentiometer. If the tubing is increased at too great a speed, the cutting is increased. If the tubing is produced at a lesser rate, the cutting is slowed.
This solution is not available when cutting perforations in dual wall tubing. The hard inner surface eliminates flexibility. Thus, tubing will not bend down or move up with the changes in production. Rather, the rate fluctuations will affect either a pulling or a pushing on the machine perforating the tubing. This is a significant problem in perforating this tubing.
An additional problem encountered in perforating tubing is the imperfect shape of most piping. When tubing is injection molded, the mold is set to produced tubing of a circular cross-section. However, due to imperfections in the mold, equipment deterioration and malfunction, or the like, the tubing produced often is not perfectly cylindrical. In circumstances where the tubing is stored on huge rollers after formation, for some period of time before perforation, sagging of the tubing tends to distort the cylindrical shape into an elliptical or oblong shape. When such misshaped tubing is fed into tubing perforating machines, such as those identified herein above, the tubing is miscut. Specifically, whole sections of tubing are skipped, while the sections that are cut are not properly cut, i.e. perforations occur in the crown of the corrugation and not in the valley of a corrugation. Since this is a circumstance that occurs with regularity, it is incumbent to have a device which can perforate piping of imperfect dimensions.
Another problem related to misshapen tubing is tubing shrinkage. When corrugated tubing is injection molded, plastic resins, often salvaged from scrap or waste plastic, such as soft drink bottles, are melted and recast into the desired tubing shape. However, as is known, different resins will shrink varying amounts when the extruded tubing cools. This can lead to tubing of diameters slightly less than that anticipated by the perforating machine. This difference will affect the perforation of the tubing, absent means for adjusting to changes in tubing flow.
An additional factor of importance in perforating tubing is the deployment of the perforations. It is often desired for certain usages to deploy the perforations in evenly separated rows around the tubing. For example, six rows of perforations would be deployed at an angular spacing of 60 degrees between each row. However, in certain environments, it may be desirable to control the displacement of the perforations. For example, some European communities prohibit piping having perforations in the bottom third of the tubing to prevent dirt from entering the tubing. Due to buying practices that have become common, other people desire tubing with a minimum number of perforations, i.e. six or eight rows. Therefore, for a truly versatile perforation machine, it must be capable of handling different perforation specifications.
Therefore, it is a purpose of the present invention to provide a perforating apparatus that can adapt to slight variations in tubing size due to shrinkage of plastic resins.
It is a further purpose of the present invention to provide an apparatus for perforating tubing which can accommodate and cut tubing of an oblong or misformed cylindrical shape.
It is a still further goal of the present invention to cut tubing of higher rigidity, such as dual wall tubing.
It is a still further purpose of the present invention to provide a tubing perforator which can effect cuts in rows disposable at any setting desired.
It is to these ends that the present invention is directed.